24.2B ESSENTIAL AMINO ACIDS For adult humans there are eight essential amino acids. These are designated with the superscript e in above table 24.2C AMINO ACIDS AS DIPOLAR IONS Since amino acids contain both a basic group(NH2)and an acidic group(-COOH), they are amphoteric h N CHCO H -hn+CHCo HNCHCO +h +h R R R Cationic form Dipolar ion Anionic form (阳离子形式) (两极离子) (阴离子形式)24.2B ESSENTIAL AMINO ACIDS For adult humans there are eight essential amino acids. These are designated with the superscript e in above table. 24.2C AMINO ACIDS AS DIPOLAR IONS Since amino acids contain both a basic group (-NH2) and an acidic group (-COOH) , they are amphoteric. H3 N + CHCO2 H R H3 N + CHCO2 - R - H + + H + - H+ + H+ H2 NCHCO2 - R Cationic form (阳离子形式） Dipolar ion (两极离子） Anionic form (阴离子形式）